The word criteria is often treated as singular or even uncountable, but these uses are usually still considered incorrect; the standard singular form is criterion. The standard and most common plural form is criteria; less common is criterions.[1][2]

^ http://www.merriam-webster.com/dictionary/criterion Merriam-Webster: "The plural criteria has been used as a singular for over half a century: let me now return to the third criteria — R. M. Nixon, that really is the criteria — Bert Lance. Many of our examples, like the two foregoing, are taken from speech. But singular criteria is not uncommon in edited prose, and its use both in speech and writing seems to be increasing. Only time will tell whether it will reach the unquestioned acceptability of agenda."

^ American Heritage: "Like the analogous etymological plurals agenda and data, criteria is widely used as a singular form. Unlike them, however, it is not yet acceptable in that use."